SPC AC 070601
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0101 AM CDT FRI AUG 07 2009
VALID 071200Z - 081200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PART OF THE
NRN/CNTRL PLNS EWD INTO THE UPR MS VLY...
...CORN BELT/UPR MS VLY...
ELEVATED CLUSTERS OF TSTMS ARE EXPECTED TO BE ONGOING EARLY FRIDAY
MORNING OVER A LARGE PART OF THE CORN BELT AND UPR MS VLY. THESE
STORMS WILL BE SUPPORTED BY CONSIDERABLE MOISTURE TRANSPORT ALONG
THE AXIS OF A 40-50 KT SSWLY LLJ. STRONGER STORMS MAY BE
ACCOMPANIED BY HAIL OR GUSTY WINDS...BUT THE PRIMARY SVR RISKS WILL
EVOLVE LATER IN THE DAY.
UPR LOW OVER THE NRN GRT BASIN IS FCST TO MOVE VERY SLOWLY EWD
DURING THE FCST PD. DOWNSTREAM UPR RIDGE WILL BUILD NWD WITH A
STOUT ELEVATED MIXED LAYER SPREADING DOWNSTREAM ACROSS MOST OF THE
PLNS/CORN BELT. THUS...WHILE SUBSTANTIAL LLVL MOISTENING IS
EXPECTED TO OCCUR ALONG/S OF THE RETREATING WRMFNT INTO THE
REGION...CONSIDERABLE CONVECTIVE INHIBITION IS ALSO EXPECTED. THIS
COUPLED WITH WEAK LARGE SCALE FORCING THROUGH MOST OF PEAK HEATING
COULD LIMIT/DELAY SFC-BASED INITIATION UNTIL NEAR EVENING.
PERSISTENT WSWLY LLVL FEED OF HOT/UNSTABLE PARCELS...APPROACH OF A
WEAK MID-LVL WAVE /CURRENTLY OVER WRN CO/ AND CONVERGENCE INVOF THE
WRMFNT COULD WEAKEN THE CAP SUFFICIENTLY FOR SFC-BASED STORM
DEVELOPMENT OVER PARTS OF CNTRL/SRN MN AND IA DURING THE EARLY
EVENING. STRONG INSTABILITY AND DEEP LAYER IN EXCESS OF 45 KTS WILL
BE FAVORABLE FOR SUPERCELLS WITH VERY LARGE HAIL AND POSSIBLY
TORNADOES. LATER IN THE PD...AS THE SWLY LLJ AGAIN
ACCELERATES...EITHER A GROWING MCS/S FROM EXISTING ACTIVITY AND/OR
NEW ELEVATED STORMS WILL FORM DOWNSTREAM INTO PARTS OF THE UPR
MIDWEST AND CNTRL GRTLKS REGION. SOME OF THIS ACTIVITY...
PARTICULARLY ALONG THE WRN FLANKS OF DEVELOPING MCS/S...WILL CONTAIN
HAIL/HIGH WINDS RISKS.
...NRN/CNTRL PLNS...
A SEPARATE REGION OF SVR POTENTIAL WILL EVOLVE ACROSS THE NRN/CNTRL
PLNS FRIDAY AFTN/EVE. A LEAD MID-LVL WAVE EJECTING NWD INTO THE NRN
HIGH PLNS EARLY FRIDAY WILL SUPPORT CONSIDERABLE CONVECTION ACROSS
CNTRL/ERN MT AND PARTS OF ND/SD EARLY IN THE PD. LOW PROBABILITIES
OF HAIL/GUSTY WINDS MAY ACCOMPANY SOME OF THIS ACTIVITY. MORE
SUBSTANTIAL SVR THREATS SHOULD DEVELOP DURING THE AFTN/EVE ACROSS
ERN MT AND EVENTUALLY FARTHER E IN THE CNTRL DKTS.
LLVL MOISTURE WILL CONTINUE TO WRAP WNW ALONG THE RETREATING WRMFNT
AND WWD ALONG NRN PERIPHERY OF A LEE LOW INTO ERN MT WITH MID-50S TO
MID-60S F SFC DEW POINTS LIKELY. TSTMS WILL PROBABLY DEVELOP EARLY
IN THE AFTN ALONG THE MOUNTAINS OF MT/WY AS LARGE SCALE HEIGHT FALLS
EDGE EWD ALONG THE DIVIDE. MLCAPE OF 1000-1500 J/KG...STEEP LAPSE
RATES AND MODEST VERTICAL SHEAR WILL CONTRIBUTE TO HIGH-BASED
SUPERCELLS WITH LARGE HAIL/DMGG WIND GUSTS. AS STORMS DEVELOP ENE
ATOP INCREASING MOIST UPSLOPE FLOW WILL PROBABLY LEAD TO STRONGER
STORMS DURING THE LATE AFTN OVER ERN MT WITH DEVELOPMENT INTO
LEWPS/BOWS.
MEANWHILE...DOWNSTREAM...OTHER STORMS WILL DEVELOP ALONG NRN EDGE OF
A LLVL DRY SLOT/TRIPLE POINT OVER WRN SD NWD ALONG AN
INVERTED-TROUGH INTO WRN ND. HERE...INSTABILITY WILL BE
COMPARATIVELY STRONGER THAN FARTHER W WITH MLCAPES TO 3000 J/KG.
SUPERCELLS WILL BE LIKELY AMID 40-45 KTS OF DEEP LAYER SHEAR AND
MID-LVL LAPSE RATES AOA 7.5 C PER KM AND VERY LARGE HAIL WILL BE
POSSIBLE. A COUPLE OF TORNADOES ARE ALSO POSSIBLE...PARTICULARLY
ACROSS NCNTRL SD INTO CNTRL ND INVOF THE SFC BOUNDARY/LOW.
..RACY/JEWELL.. 08/07/2009
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